Semiconductor storage devices such as a NAND flash memory have been downscaled to increase storage capacities. To realize further downscaling, development of memories using new materials is progressed. For example, new memories such as a ReRAM (Resistance Random Access Memory), a PRAM (Phase-Change RAM) or a PCM (Phase-Change Memory), an iPCM (interfacial PCM), a FeNAND (Ferroelectric NAND-type memory), and an MRAM (Magnetic Random Access Memory) have been developed.
These new memories are of a type in which data is written or read by flowing a current to memory cells through a clamp transistor. Conventionally, however, because a reference potential to be used for data read is generated independently of the memory cells, the reference potential is set to a constant level completely regardless of variations in characteristics of the memory cells. Therefore, different levels of the reference potential need to be generated to correspond to the variations in the characteristics of the memory cells.